Epoxy resins are employed for a wide range of applications such as electronic components, electrical equipment, automotive parts and sporting equipment since the epoxy resins have desirable properties such as adhesiveness, heat resistance and moldability. Flame-retardant agents, in particular brominated epoxy resins compounds are employed for copper-clad laminates and sealants that are used in electronic components and electrical equipment. However, halogen-containing compounds cause concerns about environment and human safety, and therefore flame-retardant agents that are more environmentally friendly are desirable.
Types of flame retardants that are perceived to be more environmentally friendly include organo-phosphorous flame retardants. In the field of epoxy resins and laminates, organo-phosphorous flame retardants with reactive groups, such as those derived from 9,10-Dihydro-9-Oxa-10-Phosphaphenantrene-10-oxide (DOPO), are typically used in epoxy resin formulations because they react with the epoxy to form a phosphorus-modified epoxy resin. The technology for producing phosphorus-modified epoxy resins and their uses, including their use in forming prepregs, laminates and copper-clad laminates is well known in the art. See for example U.S. Pat. Nos. 5,036,135; 5,364,893; 5,376,453; 5,587,243; 5,759,690; 5,817,736, 6,291,626 B1; 6,291,627 B1; 6,296,940 B1; 6,353,080 B1; 6,403,220 B1; 6,403,690 B1; 6,486,242 B1; and WO 01/42359 A1 as published in English on Jun. 14, 2001.
However, “additive” organophosphorus flame retardants, which do not have reactive groups, are typically not used in epoxy formulations, since it is believed that covalent bonding between the epoxy resin and a reactive organophosphorus flame retardant are needed to provide high glass transition temperatures and dimensional stability. The present invention relates to the use of additive flame-retardants derived from DOPO and their use in epoxy resin formulations.